1. Field of the Invention
The present invention relates to an apparatus and method for insulating containers and container stock material. In particular, the present invention relates to an insulated, paper-based beverage or food container or stock material having improved insulation properties and a method of producing these insulated containers or stock materials.
2. Description of the Background Art
Current standard paper cup stock permits excessive heat transfer through the wall of an insulated beverage container. Accordingly, a user's hand becomes uncomfortably or sometimes even painfully hot when excessive heat transfer is permitted through the container wall. This may require the user to be inconvenienced by having to release the container due to the excessive heat of the container's contents. Thus, such containers have a low hold time. An analogous but opposite situation can occur with very cold beverages, where heat from a user's hand is transferred rapidly to the contents of the container.
U.S. Pat. No. 4,435,344 to Ioka describes a method for producing an insulating composite paper container having a body member and a bottom member. The body member is formed of paper coated or laminated with a thermoplastic synthetic resin film. A surface of the body member is then heated to form a foamed polyethylene heat-insulating layer on either or both of the inner and outer surfaces of the container's body member. The heat-insulated body member is then attached to the bottom member.
U.S. Pat. Nos. 6,030,476 and 5,840,139 to Geddes et al. describe a method for producing insulating beverage containers or cups, stock material and containers made therefrom. A stock material includes a base layer, an insulating layer formed on a portion of the base layer, and a printed pattern/mineral oil applied to the insulating layer. The insulating layer is formed using a thermoplastic synthetic resin film. Also, U.S. Pat. No. 6,030,476 describes a polyethylene foam on the outside surface of the paper cup.
European Patent Application EP 0940240 A2 describes a heat insulating paper cup with targeted insulation in areas where printed matter exists. The body member of the cup is coated on its outside surface with a foamable synthetic resin and on its inside surface with a synthetic resin laminate to prevent liquid penetration. The bottom panel member is optionally coated on its upper surface with a foamed or an unfoamed synthetic resin. Printed matter is provided prior to foaming of the synthetic resin on the outer surface of the cup with water-based ink. Further, the low density polyethylene is foamed by vaporizing the water contained in the paper stock.
European Patent Application EP 1060879 A2 describes a heat insulating paper cup having a body member partially or fully coated on its outside surface with a foamed low density polyethylene and coated on its inside surface with an unfoamed modified low density polyethyelene.
However, the present inventors have determined that the devices and methods of the background art suffer from the following disadvantages. Other designs sacrifice the outside printability of the cup to provide insulation or do not provide adequate insulation properties.
The background art has not yet achieved insulated paper stock that is capable of effectively impeding heat transfer between the contents of the container and the exterior. In addition, adequate thermal insulation is not achieved from the background art in a manner that is cost effective.